This application relates generally to fiber-optic communications and more specifically to techniques for subnetwork protection in optical networks, for example, by deploying diverse routing of optical wavelengths during fiber optic or other equipment failure.
Fiber optics have become the backbone of long-haul telecommunications and as the demand for communication bandwidth has increased, fiber-optic systems have entered the metropolitan and regional telecommunications arena. Fiber-optic networks can provide the enormous bandwidth demanded by the Internet, television, and tele-video. For example, optical fibers exhibit relatively low loss in the wavelength region of 850-1675 nanometers. This particular region provides a bandwidth of about 170,000 GHz, sufficient for approximately 29 million television channels (6 MHz per channel). Although, such density is not practical to achieve, nonetheless a strong impetus is provided for the creation of all optical telecommunication networks.
Fiber-optic telecommunications networks are currently deploying a relatively new technology called dense wavelength division multiplexing (DWDM). In DWDM, several communication channels are superimposed on respective closely spaced carrier wavelengths, which are then combined (multiplexed) onto a single fiber. Today DWDM systems employ up to 80 channels, with more promised for the future.
Fiber-optic telecommunication networks deploying DWDM route optical wavelengths between users through a large variety of optical and opto-electronic devices and in a variety of standard formats. In routing optical channels between users, optical wavelengths are added to a network from a user and dropped (i.e., diverted) from the network to other users. Systems that perform these adding and dropping functions are called optical add-drop multiplexers (OADMs). OADMs can also perform adding and/or dropping functions between networks. Other routing functions may be performed, for example, by optical cross connects. One variety of optical cross connect called wavelength-selective cross connects (WSXC) can route selected subsets of optical channels onto a given path while routing other selected subsets to other paths. Several other devices such as drop-and-repeats (also known as drop-and-continues), amplifiers, and regenerators, as well as numerous other devices are used in optical networking to ensure channels are properly routed between users and to ensure that channels maintain a high level of integrity as they traverse various networks, subnetworks, and components.
The most widely adopted standard formats for optical communications include the Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) formats. SONET is the standard adopted for North America and SDH is the international counterpart. The SONET/SDH standards specify optical frequency domains, standard data rates, topological structures for optical networks, as well as other standards for communication such as data transmission formats and the like. Standard frequency domains include those set by the International Telecommunications Union (ITU) as well as other frequency bands yet to be adapted by the ITU. Standard data modulation rates vary from the lower OC-1 data rate of 51.84 Mbit/s to the much higher OC-768 rate of 40 Gbit/s, rates in between are also specified. The lower rates were chosen to handle existing electronic telecommunication signal rates while the higher rate of 40 Gbit/s is not yet commonly used.
One of the network topologies specified by the SONET/SDH standards is that of a ring. This standard differs from older topologies commonly used for electronic telecommunications and regional optical networks, which typically used hub-and-spoke and/or branching systems. SONET/SDH ring topologies are currently used in several communication domains, for example, in the access/regional and metro domains
SONET/SDH standards provide extensive protection schemes for ring failures. Protection is typically implemented in a redundant ring, often referred to as a protection ring. Protection rings are typically diversely routed from working rings. Diverse routing provides protection, for example, from the errant backhoe breaking both the working and protection ring in a single scoop of its bucket. Upon the breaking of a working ring, optical wavelengths may be diverted from the working ring to the protection ring. Various diverting mechanisms include line switching, path switching and the like.
While SONET/SDH standards provide protection schemes for a wide range of failures, industry has yet to provide solutions to implements all aspects of the protection schemes. Accordingly, industry continues to strive to develop solutions to implement the protection schemes specified by the SONET/SDH standards. For example, industry continues to strive to provide solutions for failures in multiple domains (e.g., metro network and ultra-long-haul subnetwork) that may leave a network without diverse routing and thus leave users without service. Consequently, new apparatus are needed to ensure communication does not stop in the event of failures in multiple network domains.